This invention relates generally to control of shoreline erosion by wave action, and particularly to durable, adaptable, and relatively low cost means for preventing erosion, and re-building beaches which have already been eroded.
Erosion of beaches is an old problem common to shoreline property everywhere. During storms, sand, gravel, dirt, clay and other sedimentary materials in the beaches, and in the banks and the bluffs behind the beaches, are washed away. Entire beaches disappear and buildings slide into the water when the bluffs and banks on which they are built are undermined. The problem feeds on itself. As a beach is lowered by wave action, erosion accelerates.
Undermining of bluffs and banks and sea walls is especially serious if buildings are supported on or near them. Among the factors which contribute to bluff and bank erosion are the following: natural weaknesses of some bluff materials as for example when they contain substantial percentages of clayey ingredients; ground water seeps and springs; periodically high water levels; artificially oversteepened slopes; loss of protective vegetation; capture and loss of littoral drift materials by man-made shore structures; and lack of natural shore protection (beaches) due to loss of sand and gravel.
Many conventional devices and techniques have been developed for protecting shorelines from erosion, but all have drawbacks and disadvantages. One involves making a sea wall at the shoreline, or an offshore breakwater, from massive blocks of stone or concrete, or timbers, which absorb wave energy by direct impact. If the mass is great enough and well enough anchored on a solid, deep foundation to withstand severe wave and ice conditions, these structures are generally effective. Other types are intended to channel waves into or through a series of openings or chambers in order to dissipate wave energy. These tend to be fragile and susceptible to damage and become ineffective when the openings and chambers become clogged with ice, timbers and debris and are subjected to freezing and thawing cycles. Both types are expensive and difficult to construct and maintain, and in some cases, while protecting the intended property, they create littoral currents or deflect the natural wave action to accelerate shoreline erosion on neighboring properties. Further, they are simply too expensive to be practical to protect the great bulk of beaches and shorelines which are steadily disappearing around the world.
Proposals for less expensive breakwaters made up of concrete modular units placed edge-to-edge in the water in a line parallel to the beach have been made and there are a few experimental installations of these. They have an advantage in that they can be placed rapidly by helicopter or barge or shore-based cranes at a cost which should be attractive to many property owners who otherwise could not justify the cost of conventional, massive sea walls and breakwaters.
One substantial limitation of these prior structures is that they are not really very effective in reversing the effects of erosion and re-building beaches once erosion has occurred, in spite of claims advanced for them.